Process for the preparation of 5-cyanophthalide is disclosed which comprises reacting a pharmaceuticallyacceptable salts of 5-carboxyphthalide with an alkyl carbomate to obtain 5-carboxycarbomyl phthalide. Latterwas reacted with 30% HBr in acetic acid to obtain an amide. The latter is further reacted with a chloride so as toobtain substantially pure 5-Cyanophthalide.